Adult Neurogenesis- The Brain That Grows

When you first start to learn science in grade school, everything seems so set in stone.  The teachers say "this is how it is" and you just take them at their word.  But real science is nowhere near that stagnant.  In fact, the last 20 years have seen the discovery of one of the most intriguing aspects of neural development- adult neurogenesis.

Can you believe people used to think you could tell
personality traits of a person by examining their
skull shape? 

Up until the early 1990s, most scientists believed that after the initial growth of the brain and central nervous system, usually defined as the prenatal period, the adult brain produced absolutely no new neurons.

The reasoning for such a theory is relatively sound.  Based on the most obvious observations, the adult brain undergoes no major physical changes.  Once the basic structures are set, any larger structural alterations could possibly hamper the circuits which already exist.  Imagine a city with a simple grid-pattern of streets.  That would be the adult brain.  Most scientists saw the addition of neurons as adding roads on top of those existing and through an unordered method.  It would create a mess of traffic- both in the city example and in the neural system.

Here's an example of one of the cellular
stains used to test for neurogenesis.

The second reason neurogenesis was not believed to exist was because it's relatively difficult to spot cells dividing.  It took many attempts to devise a process to definitively show cell division in the allocortex.  To tag the cells, show them dividing, and prove that these were actual progenitor cells of neurons required several techniques including Brdu labeling, studies of canary's song, and radioactively tagged thymidine in DNA synthesis.

But all this work has undeniably demonstrated adult neurogenesis truly occurs in at least two regions of the brain.  The hippocampus' dentate gyrus isn't that surprising considering its role in memory consolidation.  The other core area of neurogenesis is the subventricular zone which is the tissue lining of the brain's ventricles- cavities in the center of the brain filled with cerebrospinal fluid.

However, there's still areas of research to be discovered.  I'm curious to see what papers in the future will have to say about our ability to grow new brain cells after that first spurt of development.